Method for preparing polysuccinimides using a rotary tray dryer

ABSTRACT

A method for producing polysuccinimides is provided. A rotary tray dryer operating at an internal temperature of from about 110° to about 300° C. and providing a residence time of from about 1 hour to about 10 hours is used in the polycondensation of one or more amino acids, amic acids or ammonium salts of monoethylenically unsaturated dicarboxylic acids to produce polysuccinimides.

This is a divisional of application Ser. No. 911,867, filed Jul. 10,1992, now U.S. Pat. No. 5,319,145, issued Jun. 7, 1994.

FIELD OF THE INVENTION

The present invention relates to a process for the manufacture ofpolysuccinimides and poly(amino acids), preferably poly(aspartic acid)and copolymers thereof using a rotary tray dryer.

BACKGROUND OF THE INVENTION

Poly(amino acids) such as poly(aspartic acid) are useful as additivesfor fertilizers, scale inhibitors, detergents, pigment and mineraldispersants, and corrosion and scale inhibitors in boilers and coolingtowers. Poly(amino acids) have been synthesized by hydrolyzing theproducts of thermal polycondensation reactions of amino acids.Unfortunately, the known methods for the synthesis of poly(amino acids)are complex, expensive, or require excessively long process times.

A method for the synthesis of poly(aspartic acid) is disclosed in U.S.Pat. No. 4,839,461 to Boehmke. This process combines maleic acid ormaleic anhydride and an ammonia solution in a molar ratio of 1:1-1.5.The mixture is then heated to 120°-150° C. and the resulting solution ofammonium salt and maleic acid is evaporated, leaving a crystal mash. Thecrystal mash is then melted, during which time the waters ofcondensation and crystallization distill off. A porous mass ofpoly(aspartic acid) results. The entire process requires six to eighthours to complete.

Another method for the synthesis of poly(amino acid) is disclosed inU.S. Pat. No. 5,057,597 to Koskan, et al. This process requiresfluidizing an amino acid by agitation in a nitrogen atmosphere at atemperature of at least 180° C. for three to six hours. The resultantanhydropolyamino acid is then hydrolyzed to a poly(amino acid).

The prior art methods for the synthesis of polysuccinimides andpoly(amino acids) are time consuming, complex or use large volumes ofvolatile organic solvents or inert gases. As used hereinafter and in theappended claims, "polysuccinimides" refers to polymeric materials whichcontain succinimide moieties in the polymer chain and may contain othermoieties, and "polysuccinimide" refers to polymeric materials whichcontain only such moieties.

It is an object of this invention to provide a relatively simple processfor the manufacture of polysuccinimides which can then be hydrolyzed toform poly(amino acids).

It is a further object of the present invention to provide a continuousprocess for preparing polysuccinimides.

SUMMARY OF THE INVENTION

The present invention provides a process for producing polysuccinimidesby introducing into a rotary tray dryer one or more compounds selectedfrom amino acids, amic acids and ammonium salts of monoethylenicallyunsaturated dicarboxylic acids, operating the rotary tray dryer so as toprovide an internal temperature of from about 110° to about 300° C. anda residence time of from about 1 hour to about 10 hours, and removingthe water formed by condensation of the one or more compounds.

DETAILED DESCRIPTION OF THE INVENTION

The amino acids which can be used in the present invention includeaspartic acid, alanine, asparagine, glycine, glutamic acid, lysineglutaric acid and combinations thereof. Preferred amino acids includeaspartic acid, glutamic acid and combinations thereof. The amic acidswhich can be used in the present invention are the monoamides ofmonoethylenically unsaturated dicarboxylic acids. Suitable amic acidsinclude the monoamides derived from ammonia or primary amines and theacid anhydride, esters or acyl halides of monoethylenically unsaturateddicarboxylic acids and combinations thereof. Preferably, the amic acidsare maleamic acid (the monoamide of maleic acid), methylenesuccinamicacid (the monoamide of itaconic acid), and the monoamides of mesaconicacid, methylenemalonic acid, fumaric acid, citraconic acid, aconiticacid, alkylmaleic acids, alkenylsuccinic acids and combinations thereof.The most preferred amic acids are maleamic acid, methylenesuccinamicacid and combinations thereof. The ammonium salts of monoethylenicallyunsaturated dicarboxylic acids which can be used in the presentinvention are the partial and complete ammonium salts ofmonoethylenically unsaturated dicarboxylic acids. Suitable ammoniumsalts of monoethylenically unsaturated dicarboxylic acids include thepartial and complete ammonium salts of maleic acid, itaconic acid,mesaconic acid, methylenemalonic acid, fumaric acid, citraconic acid,aconitic acid, alkylmaleic acids, alkenylsuccinic acids and combinationsthereof. The preferred ammonium salts of monoethylenically unsaturateddicarboxylic acids are the ammonium salts of maleic acid.

The rotary tray dryers useful in the present invention are, for example,those taught in U.S. Pat. No. 3,728,797 to Worden, et. al., incorporatedby reference herein. Particularly suitable are continuous rotary traydryers of the type manufactured under the trademark TURBO-Dryer by theWyssmont Company, Inc., assignees of the aforementioned patent.Continuous rotary tray dryers deliver material to an upper tray in thedryer through an inclined chute, and thereafter transfer the materialthrough the dryer from tray to tray by passing it through inclinedchutes which extend between vertically adjacent trays. Upon rotation ofthe trays, wiper arms associated with each tray guide the material overthe laterally outer edges of the trays and into the upper ends of theinclined chutes, while additional wiper arms and leveler arms associatedwith each tray distribute the material transferred to the tray from thenext highest tray evenly over the surface of the tray. Thus, thetransfer of the material through the dryer is very gentle, and resultsin negligible breakage, minimum formation of fines and minimum adhesionof the material to the trays or to the transfer arms and chutes.

The polysuccinimides are produced by a thermal polycondensationreaction. The process utilizes heat and mild agitation to condense andpolymerize the one or more amino acids, amic acids or ammonium salts ofmonoethylenically unsaturated dicarboxylic acids. The polycondensationreactions typically proceeds by polymerizing these compounds to form ananhydropolyamino acid by driving off the water formed fromintermolecular condensation of these compounds as well as from internalcyclization. Thus, the water liberated during the reaction must beremoved in order to drive the reaction toward completion. Thepolysuccinimides which results from the polycondensation of the one ormore amino acids, amic acids or ammonium salts of monoethylenicallyunsaturated dicarboxylic acids can be used as is, or they can behydrolyzed, preferably using alkaline hydrolysis, to form a poly(aminoacid).

The process utilizes conventional equipment that is commerciallyavailable to provide the mild agitation and heat required to manufacturepolysuccinimides. Any rotary tray dryer that provides both mildagitation and heat is suitable for use in this process. The mildagitation provides contact of the one or more amino acids, amic acids orammonium salts of monoethylenically unsaturated dicarboxylic acids withthe growing polymer chains, assists in driving off the water formed fromthe polycondensation reaction, improves heat transfer and allows forshorter reaction times. The mild agitation occurs when the materialfalls between the vertically adjacent trays and when the material isleveled by the wiper blade. The rotary tray dryer is operated such thatmaterial is transferred between vertically adjacent trays at intervalsof from about 1 minute to about 30 minutes. Furthermore, a sufficientnumber of trays must be present in the rotary tray dryer to provide aresidence time for the material being polymerized of from about 1 hourto about ten hours. Mild agitation further reduces the loss of productand the risks associated with dusty, airborne materials.

The rotary tray dryer is equipped with a heating means, such as a heatjacket, internal heating coils or both, which provides heat for thepolycondensation of the one or more amino acids, amic acids or ammoniumsalts of monoethylenically unsaturated dicarboxylic acids. Thepolycondensation is performed at an internal temperature of from about110° to 300° C. Preferably, the internal temperature is at least 120° C.for the polycondensation of one or more ammonium salts ofmonoethylenically unsaturated dicarboxylic acids, at least 120° C. forthe polycondensation of one or more amic acids, and at least 200° C. forthe polycondensation of one or more amino acids.

The rotary tray dryer can be operated under subatmospheric, atmosphericor superatmospheric pressure. It is preferred to operate at atmosphericor subatmospheric pressure to assist the removal of water formed fromthe polycondensation reaction. The removal of water is also assisted bypassing a continuous stream of air or nitrogen through the rotary traydryer. Preferably, the polycondensation is conducted at atmosphericpressure with a continuous stream of heated air passing through therotary tray dryer.

The following examples are embodiments of the general process discussedhereinabove and are intended by way of illustration only and are notintended to limit the invention in any way.

EXAMPLE 1

A 2-tray dryer having a movably positioned top tray and a movablypositioned bottom tray wherein the vertical positions of the two trayscould be switched, was pre-heated to provide an internal temperature of240° C. and a continuous stream of heated air flowing at a rate of 300cubic feet/minute was passed through the dryer. 1000 grams of L-asparticacid was introduced into the top tray of the dryer, and the bed depthwas adjusted to 1.5 inches. The material in top tray was transferred tothe lower tray every ten minutes, then the vertical positions of thetrays were switched. After 50 minutes, the bed depth was changed to 1.25inches. After 70 minutes, the temperature of the material in the trayshad reached 230° C. and the air flow was reduced to 250 cubicfeet/minute. The total residence time was 6 hours. Analysis by ¹ H NMRspectroscopy indicated that greater than 95 percent by weight of theaspartic acid was converted to polysuccinimide. 700 grams ofpolysuccinimide was recovered as a tan, free-flowing powder.

EXAMPLE 2

The same procedure was followed as in Example 1 except that the internaltemperature of the rotary tray dryer was 270° C. Analysis by ¹ H NMRspectroscopy indicated that the aspartic acid was completely convertedto polysuccinimide.

We claim:
 1. A continuous method for producing polysuccinimidescomprising the steps of:continuously introducing into a rotary traydryer one or more compounds selected from the group consisting of amicacids and ammonium salts of monoethylenically unsaturated dicarboxylicacids, wherein the amic acids are monoamides of monoethylenicallyunsaturated dicarboxylic acids; and wherein α-amino acids are notintroduced into the rotary tray dryer; operating the rotary tray dryerso as to provide an internal temperature of from about 120° to about300° C. and a residence time of from about 1 hour to about 10 hours; andremoving the water formed by condensation of the one or more compoundsto produce polysuccinimides.
 2. A continuous method for producingpoly(amino acids) comprising the steps of:continuously introducing intoa rotary tray dryer one or more compounds selected from the groupconsisting of α-amino acids, amic acids and ammonium salts ofmonoethylenically unsaturated dicarboxylic acids; wherein the amic acidsare monoamides of monoethylenically unsaturated dicarboxylic acids;operating the rotary tray dryer so as to provide an internal temperatureof from about 120° to about 300° C. and a residence time of from about 1hour to about 10 hours; removing the water formed by condensation of theone or more compounds to produce polysuccinimides; and hydrolyzing thepolysuccinimide to form poly(amino acids).
 3. The method of claim 2wherein the one or more α-amino acids are selected from the groupconsisting of: aspartic acid, asparagine, alanine, glycine, glutamicacid, and mixtures thereof.
 4. The method of claim 2 wherein the one ormore α-amino acids are selected front the group consisting of: asparticacid, glutamic acid, and mixtures thereof.
 5. The method of claim 2wherein the one or more α-amino acids is aspartic acid.
 6. The method ofclaim 1 or 2 wherein the one or more compounds are amic acids selectedfrom the group consisting of maleamic acid, methylenesuccinamic acid,and the monoamides of mesaconic acid, methylenemalonic acid, fumaricacid, citraconic acid, aconitic acid, and combinations thereof.
 7. Themethod of claim 1 or 2 wherein the one or more compounds are amic acidsselected from the group consisting of maleamic acid andmethylenesuccinamic acid.
 8. The method of claim 1 or 2 wherein the oneor more compounds is maleamic acid.
 9. The method of claim 1 or 2wherein the one or more compounds is methylenesuccinamic acid.
 10. Themethod of claim 1 or 2 wherein the one or more compounds are ammoniumsalts of monoethylenically unsaturated dicarboxylic acids selected fromthe group consisting of partial and complete ammonium salts of maleicacid, itaconic acid, mesaconic acid, methylenemalonic acid, fumaricacid, citraconic acid, aconitic acid, and combinations thereof.
 11. Themethod of claim 1 or 2 wherein the one or more compounds are ammoniumsalts of monoethylenically unsaturated dicarboxylic acids selected frontthe group consisting of partial and complete ammonium salts of maleicacid.
 12. The method of claim 1 or 2 wherein the one or more compoundsare ammonium salts of monoethylenically unsaturated dicarboxylic acidsand the internal temperature is at least 120° C.
 13. The method of claim1 or 2 wherein the one or more compounds are amic acids and the internaltemperature is at least 120° C.
 14. The method of claim 1 or 2 whereinthe internal temperature is at least 200° C.